playframework CRUD NullPointerException while loading classes-Collection of common programming errors

I get this Exception when running a play app that uses the crud module. the strange thing is that when i get this error and i refresh web page the play app works and page is loaded correctly. it seems the play compiler -in DEV mode- can’t compile CRUD class in first request. i don’t know why the play compiler in DEV mode frequently fails compiling some classes in my play web app?

i use eclipse IDE & i suspect that eclipse locks some java source files and prevent play from compiling the java sources ; however i’m not sure of this. There might be some reason that causes play DEV mode compiler to fail & i can’t figure it out. this issue is happening to me a lot these days while working on a play web app.

what this error means and how to fix it?

ERROR ~ 

@69g88ea66
Internal Server Error (500) for request GET /

Template execution error (In {module:crud}/app/views/tags/crud/types.tag around line 3)
Execution error occured in template {module:crud}/app/views/tags/crud/types.tag. Exception raised was NullPointerException : null.

play.exceptions.TemplateExecutionException
    at play.templates.BaseTemplate.throwException(BaseTemplate.java:86)
    at play.templates.GroovyTemplate.internalRender(GroovyTemplate.java:257)
    at play.templates.GroovyTemplate$ExecutableTemplate.invokeTag(GroovyTemplate.java:379)
    at /conf/routes.(line:42)
    at play.templates.GroovyTemplate.internalRender(GroovyTemplate.java:232)
    at play.templates.Template.render(Template.java:26)
    at play.templates.GroovyTemplate.render(GroovyTemplate.java:187)
    at play.mvc.Router.parse(Router.java:162)
    at play.mvc.Router.load(Router.java:48)
    at play.mvc.Router.detectChanges(Router.java:219)
    at Invocation.HTTP Request(Play!)
Caused by: java.lang.NullPointerException
    at play.classloading.ApplicationCompiler$2.acceptResult(ApplicationCompiler.java:266)
    at org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:478)
    at play.classloading.ApplicationCompiler.compile(ApplicationCompiler.java:282)
    at play.classloading.ApplicationClassloader.getAllClasses(ApplicationClassloader.java:424)
    at play.classloading.ApplicationClassloader.getAssignableClasses(ApplicationClassloader.java:453)
    at play.classloading.ApplicationClassloader$getAssignableClasses.call(Unknown Source)
    at {module:crud}/app/views/tags/crud/types.tag.(line:3)
    at play.templates.GroovyTemplate.internalRender(GroovyTemplate.java:232)
    ... 9 more

—————UPDATE—————-

CRUD routes that i use in routes file. do i need to delete them ?

#{crud.types}
GET         /?                                          ${type.controllerClass.name.substring(12).replace('$','')}.index
GET         /${type.controllerName}                     ${type.controllerClass.name.substring(12).replace('$','')}.list
GET         /${type.controllerName}/new                 ${type.controllerClass.name.substring(12).replace('$','')}.blank
GET         /${type.controllerName}/{id}                ${type.controllerClass.name.substring(12).replace('$','')}.show
GET         /${type.controllerName}/{id}/{field}        ${type.controllerClass.name.substring(12).replace('$','')}.attachment
GET         /${type.controllerName}/{id}/edit           ${type.controllerClass.name.substring(12).replace('$','')}.edit
POST        /${type.controllerName}                     ${type.controllerClass.name.substring(12).replace('$','')}.create
POST        /${type.controllerName}/{id}                ${type.controllerClass.name.substring(12).replace('$','')}.save
DELETE      /${type.controllerName}/{id}                ${type.controllerClass.name.substring(12).replace('$','')}.delete
#{/crud.types}